Puffer-type circuit breaker and nozzle emitting gas with coaxial abutting plastic tube

ABSTRACT

A compressed-gas circuit breaker is provided with two contacts arranged coaxially opposite one another, at least one of which can be driven to move in the axial direction. The two contacts define in the interrupted state a contact gap. The circuit breaker also has a nozzle, made of insulating material, which is connected to the driven contact and which surrounds at least part of the contact gap. The invention calls for a high-strength plastic tube abutting coaxially against the outside of the insulating nozzle in order to prevent the nozzle from expanding radially as a result of an increase in arc-extinguishing gas pressure.

FIELD OF THE INVENTION

The present invention relates to a compressed-gas circuit breaker,particularly for high voltages, with two contacts arranged coaxiallyopposite one another, at least one of which can be driven to move in theaxial direction, the two contacts defining in the interrupted state acontact gap, and with a nozzle, made of insulating material, which isconnected to the driven contact and which surrounds at least part of thecontact gap.

BACKGROUND OF THE INVENTION

Such a compressed-gas circuit breaker is known, for example, from U.S.Pat. No. 4,163,131.

In such an insulating nozzle switch circuit breaker, an intense pressurerise results after the separation of the contacts and the firing of anelectric arc due to the heating up of an arc-extinguishing gas in thearea of the contact gap, the pressure rise being used by means of thenozzle to achieve during the current zero crossing a blowout of theelectric arc and thus a supporting of the extinguishing process.

With the increasing capacity of such high-voltage circuit breakers, thearc-extinguishing gas pressure becomes so intense in the area of thenozzle made of insulating material that the risk of an expansion of thenozzle member arises. This cannot be easily counteracted by producingthe nozzle with a more stable material or with a greater wall strengthsince on the one hand the nozzle material itself is intended to releasearc-extinguishing gas under the influence of the electric arc and on theother hand the arc-extinguishing gas nozzle with the drivable contactshould be movable as quickly as possible, i.e., should have low mass, atleast during the switching off.

OBJECTS AND SUMMARY OF THE INVENTION

The underlying object of the invention is to design a high-voltagecircuit breaker of the type described in the introduction such thatdamage to the nozzle made of insulating material is avoided andnevertheless in this process the fastest possible switching speed isensured. This objective is solved according to the invention by ahigh-strength plastic tube abutting coaxially against the outercircumference of the nozzle made of insulating material in its regionexposed to the quencher gas pressure.

U.S. Pat. No. 4,786,770 discloses an insulating nozzle switch circuitbreaker in which the nozzle made of insulating material is surrounded bya magnetic ring which is provided for the purpose of producing amagnetic field that lengthens the electric arc or allows it to rotate.Such a ring is heavy and accordingly difficult to accelerate. In thepreviously known switch, this does not entail any disadvantages sincethe nozzle made of insulating material is not joined to the drivablecontact. There, the ring is also not provided for mechanicalstabilization of the nozzle made of insulating material, but is providedonly for magnetic reasons.

In contrast, the tube according to the invention stabilizes the nozzlemade of insulating material against radial expansions due to thecompressive loads produced by the expanding arc-extinguishing gas. Thehigh-strength plastic tube does not have to consist of the same materialas the nozzle made of insulating material since it does not come intocontact with the electric arc and is also not intended to release anyarc-extinguishing gas under the influence of the electric arc. Moreover,a less expensive material can be chosen than for the nozzle made ofinsulating material since the plastic tube has only mechanicalstabilization duties and can be built correspondingly small. The plastictube only needs to be large enough to brace the nozzle made ofinsulating material in the areas of particularly low wall strength.

The plastic tube can also be integrated into the nozzle member on itsouter circumference so that it protrudes as little as possible over theouter contour. This increases the dielectric stability.

An advantageous refinement of the invention provides that the plastictube consists of a fiber-reinforced plastic.

Such a fiber-reinforced plastic tube has a particularly high mechanicalstability, particularly against expansion. Aramide fibers, fiberglass orplastic fibers can be provided as reinforcement fibers.

Moreover, it can be advantageously provided that the reinforcementfibers run in the circumferential direction of the plastic tube.

In this case, the reinforcement action is particularly effective againsta radial expansion of the plastic tube.

Moreover, the invention can be advantageously developed in that theplastic tube is arranged in an area of the nozzle made of insulatingmaterial with decreased wall strength compared to other areas.

In this area, stabilization of the nozzle made of insulating material isparticularly efficient, whereas it does not seem necessary in otherregions in which the wall strength of the nozzle made of insulatingmaterial is already greater due to enlargements provided for reasons offlow engineering.

The plastic tube can also be advantageously adhered to the nozzle madeof insulating material.

This results in a secure and gap-free connection between the nozzle madeof insulating material and the plastic tube which ensures that, besidesincreased dielectric stability, even for variable thermal expansion ordue to the constant shocks during switching operations, the plastic tuberemains in its position on the nozzle made of insulating material. Theplastic tube can also be advantageously shrunk on to the nozzle made ofinsulating material.

A further advantageous refinement of the invention provides that thenozzle made of insulating material is preloaded radially inwards by theplastic tube.

The nozzle made of insulating material then tolerates higher compressiveloads in its inside particularly well since the preloading is notneutralized until an increased compressive load occurs and a neutralform of the nozzle made of insulating material is achieved. The nozzlemade of insulating material thus withstands particularly higharc-extinguishing gas pressures.

It can also be advantageously provided that the plastic tube ismanufactured through application of a fiber web to the nozzle made ofinsulating material and subsequent impregnation with an impregnatingresin.

In this manner, the named plastic tube can be manufactured particularlysimply and simultaneously joined securely to the nozzle made ofinsulating material.

BRIEF DESCRIPTION OF THE DRAWING

The invention is shown hereafter based on an exemplary embodiment in adrawing and subsequently described.

The FIGURE is a schematic longitudinal cross-section view of a circuitbreaker with a nozzle made of insulating material.

DETAILED DESCRIPTION

The FIGURE shows a high-voltage circuit breaker having two contacts 1, 2arranged coaxially opposite one another, of which the second contact 2can be driven in a manner not shown. The circuit breaker is shown in theinterrupted state. In the area of the contact gap 3 between the contacts1, 2, an electric arc is drawn during the break procedure that heats uparc-extinguishing gas present there, particularly SF₆ and thus increasesthe arc-extinguishing gas pressure.

The nozzle 4 made of insulating material is securely joined to themovable contact 2 so that the nozzle moves with it during the breakprocedure.

In the area of the contact gap, the nozzle 4 made of insulating materialdefines in its interior an electric arc space, resulting in storage ofhot arc-extinguishing gas under high pressure, that later flows backinto the area of the electric arc during the current zero crossing ofthe current to be switched and contributes to extinguishing of theelectric arc or rather a dielectric recovery of the contact gap 3.

This extinguishing effect is also supported by additional compressedarc-extinguishing gas that is made available in the compression space 5by the switching motion between a compression cylinder 6 and acompression piston 7. The mechanically compressed arc-extinguishing gascan then flow via the channel 8 to the contact gap 3.

The nozzle 4 made of insulating material can be produced advantageouslyfrom PTFE (polytetrafluoroethylene) since this substance releases gasesunder the influence of an electric arc that support the extinguishing ofthe electric arc.

The nozzle 4 made of insulating material bears on its outside a plastictube 9 made of fiber-reinforced plastic that is adhered to the nozzlemade of insulating material. The plastic tube 9 extends over the area ofthe nozzle 4 made of insulating material in which it is designed withparticularly thin walls.

In this manner, a radial expansion of the nozzle made of insulatingmaterial due to excessive arc-extinguishing gas pressure, e.g., due to ahigh current intensity to be switched, is avoided.

We claim:
 1. A high-voltage compressed-gas circuit breaker,comprising:two contacts arranged coaxially opposite one another, atleast one of said contacts being driveable to move in an axialdirection, said contacts defining a contact gap therebetween when in aninterrupted state; a nozzle made of insulating material, said nozzlebeing connected to the driveable contact, and said nozzle surrounding atleast part of the contact gap; and a high-strength plastic tubecoaxially positioned and abutting against an outer circumference of thenozzle at a region of the nozzle exposed to extinguishing gas pressure.2. The high-voltage circuit breaker of claim 1, wherein the plastic tubecomprises fiber-reinforced plastic.
 3. The high-voltage circuit breakerof claim 2, wherein reinforcement fibers of the fiber-reinforced plasticextend in a circumferential direction of the plastic tube.
 4. Thehigh-voltage circuit breaker of claim 1, wherein the plastic tube ispositioned in an area of the nozzle having decreased wall strengthrelative to other areas of said nozzle.
 5. The high-voltage circuitbreaker of claim 1, wherein the plastic tube is adhered to the nozzle.6. The high-voltage circuit breaker of claim 1, wherein the plastic tubeis shrunk onto the nozzle.
 7. The high-voltage circuit breaker of claim1, wherein the nozzle is preloaded radially inwards by the plastic tube.8. The high-voltage circuit breaker of claim 1, wherein the plastic tubeis manufactured through application of a fiber web to the nozzle andsubsequent impregnation with an impregnating resin.